Computer Programming Concepts and Visual Basic David I. Schneider

■ FLAGS
A flag is a variable that keeps track of whether a certain situation has occurred. The data type
most suited to flags is the Boolean data type. Variables of type Boolean can assume just two
values—True and False. Flags are used within loops to provide information that will be utilized
after the loop terminates. Flags also provide an alternative method of terminating a loop.
EXAMPLE 4
The following program counts the number of words in the file WORDS.TXT and then reports whether the
words are in alphabetical order. In each execution of the loop, a word is compared to the next word in the
list. The flag variable, called orderFlag, is initially assigned the value True and is set to False if a pair of
adjacent words is out of order. The technique used in this program will be used in Section 6 when we study
sorting. Note: The statement in line 7, word1 = “”, is a device to get things started. Each word must first
be read into the variable word2.
WORDS.TXT contains the following winning words from the U.S. National Spelling Bee:
“cambist”, “croissant”, “deification”
“hydrophyte”, “incisor”, “maculature”
“macerate”, “narcolepsy”, “shallon”
Object Property Setting
frmWords Caption Word Analysis
cmdAnalyze Caption Analyze Words
picReport
Private Sub cmdAnalyze_Click()
Dim orderFlag As Boolean, wordCounter As Integer
Dim word1 As String, word2 As String
‘Count words. Are they in alphabetical order?
orderFlag = True
wordCounter = 0
word1 = “”
Open “WORDS.TXT”For Input As #1
Do While Not EOF(1)
Input #1, word2
wordCounter = wordCounter + 1
If word1 > word2 Then ‘Two words are out of order
orderFlag = False
End If
word1 = word2
Loop
Close #1
picReport.Print “The number of words is”; wordCounter
If orderFlag = True Then
picReport.Print “The words are in alphabetical order.”
Else
picReport.Print “The words are not in alphabetical order.”
End If
End Sub
[Run, and press the command button.]
Processing Lists of Data with Do Loops 139